Leishmaniasis encompasses a broad spectrum of neglected, but important tropical diseases; yet there are no effective vaccines for any clinical forms of the disease. The major obstacle in developing an effective anti- Leishmania vaccine is insufficient information on parasite antigens that elicit protective T-cell responses and appropriate regulation, since inadequate and excessive immune responses can contribute to pathogenesis, leading to vaccine failure. Our studies in animal models have revealed detrimental and protective immune responses programmed at the initial stages of infections with L. amazonensis and L. braziliensis, respectively. We hypothesized that vaccination with rationally selected T-cell antigens of L. braziliensis, together with appropriate adjuvants, can elicit a broad-spectrum and high-quality T-cell immunity for the control of American cutaneous leishmaniasis. This hypothesis will be tested in two Specific Aims. Aim 1 will examine whether L. braziliensis candidates identified through an immunoinformatics approach can cross-protect mice against another New World Leishmania spp infection. The immunogenicity and vaccine potential of the top three candidates will be tested via DNA- and protein-based immunization regimens, in conjunction with novel TLR4- adjuvants glucopyranosyl lipid A (GLA) and monophosphoryl lipid A (MPL). Aim 2 will test the hypothesis that the level of protection offered by various vaccines positively correlates with the quality and spectrum of T-cell responses. In vitro and in vivo assays will be used to analyze the frequency of multi-functional CD4+ T effector and memory cells during immunization and parasite challenge. We will examine the molecular basis of protection induced by vaccine immunization and chemotherapy. The long-term goal of this study is to define the protective mechanisms associated with Leishmania infection and to utilize this information for the design of control strategies for this and other persistent parasitc infections. The innovation of this study is our comprehensive approaches for identifying new T-cell antigens of L. braziliensis and evaluating T-cell quality and cross-species protection. This study is highly relevant to the rational vaccine design for non-healing leishmaniasis, but also has broad implications for other chronic diseases caused by intracellular pathogens.